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FAIR VALUE MEASUREMENTS - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Apr. 18, 2024	Apr. 15, 2024	Apr. 01, 2024	Dec. 31, 2023
Fair Value of Financial Instruments [Line Items]
Investments not required to be disclosed	$ 408					$ 382
4.70% $500 Million Unsecured Notes | Subsequent Event | Senior Notes | JCP&L
Fair Value of Financial Instruments [Line Items]
Face amount of debt					$ 500
Issuance interest rate					4.70%
7.375%, 715 Million Notes due 2031 | Senior Notes
Fair Value of Financial Instruments [Line Items]
Face amount of debt	$ 463
Issuance interest rate	7.375%
Make-whole premium	$ 80
4.10% $400 Million First Mortgage Bond | Subsequent Event | Senior Notes | JCP&L
Fair Value of Financial Instruments [Line Items]
Face amount of debt				$ 400
Issuance interest rate				4.10%
5.94% $250 Million Unsecured Notes | Subsequent Event | Senior Notes | MAIT
Fair Value of Financial Instruments [Line Items]
Face amount of debt			$ 250
Issuance interest rate			5.94%
Corporate-Owned Life Insurance
Fair Value of Financial Instruments [Line Items]
Gain (loss) on investments	$ 9	$ 7

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